The present invention relates to subassemblies of contactor-separator units suitable for use in liquid-liquid or gas-liquid exchange or extraction apparatus.
There exist numerous extraction or exchange processes which require a number of successive operations each successively involving intimate contact between two immiscible fluids and separation between the fluids. Examples of such processes are isotopic enrichment by exchange between two liquid phases containing uranium in different valence states, for instance VI and IV. Another example is separation of rare earths, which may require several hundred of mixing-settling operations for achieving the required purity.
Referring to isotopic enrichment as an example, each elementary contact-separation sequence provides an enrichment, however, with a low partition coefficient, whereby a large number of operations is necessary for achieving the desired enrichment. A large number of contactor-separator units is consequently necessary, in which counter-current flows of two phases occur. In the conventional cascades, one pump for each stage or unit is provided, resulting in high investment and maintainance costs as well as difficult monitoring and control.
The same problem is associated with, for instance, for extraction of deuterium oxide or heavy water, in which ejectors are used drawing gas into a water jet and forming an intimate mixture which is later separated. A plurality of ejectors should be located in series relation to achieve the desired enrichment and each ejector is associated with a separate pump.
It is also known that technology or efficiency reasons limit the flow rate acceptable in a line of contactor-separator units. If a higher flow rate is required, a plurality of lines, each consisting of a plurality of contactor-separator units in series relation, are located in parallel flow relation. But this solution requires the number of pumps to be multiplied by the number of series disposed in parallel.
It is an object of the present invention to remove the need for such a multiplication of the number of pumps in an installation having several series located in parallel, while retaining the advantages of such an arrangement.
According to an aspect of the invention, there is provided a sub-assembly for an exchange or extraction apparatus between a first and a second mutually immiscible fluid phases, typically under such conditions that the net mass transfer between the two phases is small as compared with the instantaneous rates of flow of the phases, comprising: m.times.n contactor-separator units located in a matrix arrangement of m lines and n columns, means for directing flows of the first phase to the first contactor-separator units of respective ones of said lines and directing the flow of said first phase from the outlet of each said contactor-separator unit to the inlet of the next contactor-separator unit of the same line, means for directing flows of the second phase to the first contactor-separator units of respective ones of said columns and for directing the flow of said second phase from each contactor-separator unit to the next contactor-separator unit of the same column, and m+n pumping units each associated with a corresponding line or column, providing a pressure increase corresponding to the head loss impressed to the flow by all contactor-separator units in a line or a column, respectively.
The contactor-separator units may be of any one of a number of conventional types. For instance, each may be a static mixer followed by a settler. The pumping means may be of any type providing the necessary rate of flow and pressure increase. No difficulty will be involved since the head loss impressed by a mixer-settler is typically of about 50 cm of water head.
The sub-assembly comprises m.times.n contactor-separator units in a matrix or "crossed" arrangement. Since a single pump per line and per column ensures the flow for each phase, the total number of pumps is m+n.
The partition coefficient will typically be very low, for instance for the separation of uranium isotopes; it is then necessary to have a large number of contactor-separator units to achieve the isotopic enrichment which is frequently required. Then, an installation will generally be used which comprises a plurality of sub-assemblies each having m.times.n contactor-separator units.
The number of lines and columns of the assembly may be equal or different, leading to a "square matrix" or "rectangular matrix" structure.
One or more contactor-separator sub-assembly(ies) according to the invention can also be used in the chemical or petrochemical industry, the re-processing of spent nuclear fuels as well as for isotopic enrichment of uranium.